The present invention relates to a stepping motor control apparatus that is able to detect changes in the load of the stepping motor. Consequently, the stepping motor control apparatus is able to control the rotation of the stepping motor so that it is normal. The present invention particularly relates to a stepping motor control apparatus that is able to prevent the occurrence of step-outs.
Stepping motors accurately rotate only at an angle that corresponds to the number of pulses provided, so they have characteristics such that open control is possible. The speed of rotation is determined according to the number of command pulses provided per unit time regardless of the load. Therefore, stepping motors have superior rotation precision and stopping precision and are widely used as drive motors of various precision machines.
However, stepping motors have a drawback in that when overloads above a fixed amount are in effect, step-outs occur that result in rotation stopping or rotation control becoming impossible. These step-outs are a characteristic that is not found in AC motors and DC motors. For this reason, countermeasures with respect to step-outs are required if a stepping motor is to be used.
An example of a step-out countermeasure employed in conventional stepping motors is shown for example in Japanese Unexamined Patent Application Publication H11-235092. An output shaft and a deceleration mechanism are connected via a torque sensor and an emergency stop is caused when the torque has exceeded a prescribed value.
However, in a method that mechanically detects the load that acts on the stepping motor in the conventional way, there is a problem in that as the number of components causes manufacturing costs to increase, and the electrical wiring becomes complicated.